<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>画板</title>
    <link rel="stylesheet" href="style.css">
</head>
<body>
    <canvas id="canvas" width = "100" height="100"></canvas>
    <script>
        var canvas = document.getElementById("canvas");
        canvas.width = document.documentElement.clientWidth;
        canvas.height =document.documentElement.clientHeight;/!--获取的是文档的高度而不是body的高度--/
        var ctx = canvas.getContext("2d");
        ctx.fillStyle = "black";
        ctx.strokeStyle = "#000000";//边框
        ctx.lineWidth = 10;
        ctx.lineCap = "round";

        function drawLine(x1,y1,x2,y2){
            ctx.beginPath();
            ctx.moveTo(x1,y1);
            ctx.lineTo(x2,y2);
            ctx.stroke();
        }
        let painting  = false;
        let last 
        var isTouchDevice = 'ontouchstart' in document.documentElement;
        if(isTouchDevice){
            canvas.ontouchstart = (e)=>{
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                last = [x, y]
            }
            canvas.ontouchmove = (e) =>{
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                drawLine(last[0],last[1],x,y)
                last=[x,y]
            }   
        }else{
            canvas.onmousedown = (e) =>{
            painting = true
            last = [e.clientX,e.clientY]
            console.log(last)

        }
        canvas.onmousemove = (e)=>{
            console.log(last)
            if(painting === true){
                drawLine(last[0],last[1],e.clientX,e.clientY)
                last = [e.clientX,e.clientY]
            }
        }
        canvas.onmouseup = () =>{
            painting = false
        }
        }
    </script>
</body>
</html>
